Extreme ultraviolet lithography (EUV, also known as soft x-ray projection lithography) is a contender to replace deep ultraviolet lithography for the manufacture of 0.13 micron, and smaller, minimum feature size semiconductor devices.
However, extreme ultraviolet light, which is generally in the 7 to 40 nanometer wavelength range, is strongly absorbed in virtually all materials. For that reason, extreme ultraviolet systems work by reflection rather than by transmission of light. Through the use of a series of mirrors, or lens elements, and a reflective element, or mask blank, coated with a non-reflective absorber mask pattern, the patterned actinic light is reflected onto a photoresist-coated semiconductor wafer.
Advances in photolithography techniques utilized to transfer patterns to photoresist have enabled increasingly smaller patterns to be transferred. This means that smaller integrated circuit features can be formed in integrated circuits. As a result, more elements can be put in a given area on a semiconductor integrated circuit resulting in the ability to greatly reduce the cost of integrated circuits while increasing functionality in the electronic devices in which the integrated circuits are used.
In the manufacture of semiconductor integrated circuits, a photoresist is deposited on a semiconductor wafer. On exposure to radiation and other processing, the exposed areas of the photoresist undergo changes that make those regions of the photoresist either harder or easier to remove. As a result, subsequent processing can selectively remove the easier to remove material, leaving behind the patterned, harder to remove material. This pattern can then be transferred to the semiconductor wafer via the photoresist, for example, by using the remaining photoresist as a mask for etching the desired features into the underlying layers of the semiconductor wafer.
There are many demands that are being placed on EUV photoresists because of the need to make finer and finer masks. Currently, there is no known material that simultaneously meets resolution, line edge roughness, and sensitivity (RLS) requirements for a EUV photoresist. In addition to RLS issues, conventional spin-on techniques for EUV photoresists are deficient in a number of areas.
First, spin-on photoresists are coated using a casting solvent, which can cause environmental problems.
Second, spin-on deposition techniques do not provide good thickness control and have variations in thickness in the vertical Z direction, especially as film thicknesses decrease.
Third, components of a spin-on photoresist solution may tend to segregate at the interfaces due to surface energy effects.
Thus, as EUV lithography becomes more necessary, it is increasingly critical that answers be found to these problems. Additionally, the need to reduce costs, improve efficiencies and performance, and meet competitive pressures adds an even greater urgency to the critical necessity for finding answers to these problems.
Solutions to these problems have been long sought but prior developments have not taught or suggested any solutions and, thus, solutions to these problems have long eluded those skilled in the art.